Young Scientist
I wish to be a photon juggler
Shigeki TAKEUCHI, Ph. D
B.S. and M.S. Physics Department, Kyoto University in 1991 and1993. Central Research Laboratory, Mitsubishi Electric, 1993. Lecturerof Research Institute for Electronic Science (RIES), Hokkaido University
since 1999. Ph.D. (Science) from Kyoto University, 2000. Appointed
Associate Professor of RIES in 2000. Serving concurrently as a researcher in the JST PRESTO project from 1995 to the present.

Introduction
I am an experimental physicist working
in the field of quantum optics. When I wasasked to write an article for the "young scientist" section, the editor said that any kindof topics would be welcome. Here, I'd like tooffer three topics that I hope will interest you.
The first one is my brief history. In it, you willlearn how a young scientist enjoyed doing
basic research in a private company. The second topic is about my life at Hokkaido University. Some of the readers may have heard
about the stressful life of people in Japanese
metropolises, i.e. extremely crowded commuter trains. However, life in Sapporo, whereHokkaido University is located, is completelydifferent. The third topic is our research activities relating to the quantum information
technologies using photons.

My Brief History
After I finished my master's degree inlow dimensional condensed matter physics at
Kyoto University, I entered Mitsubishi Electric
Corporation, where I wanted to do researchon quantum devices.
In the company, I belonged to the Embryonic Science and Technology Department.
That department was not very large, however, many interesting kinds of basic researchwere being conducted in the department: Research on the neural networks of sea slugs,
single molecular diodes, and so on.
Mr. Maeda, the director of the department, encouraged us to be ambitious in creative work. He gave me a chance to look fora really interesting topic, and I had an opportunity to read a paper on a quantum computation algorithm proposed by Deutsch andJozsa.

An idea struck me that an experimentdemonstrating the algorithm was possible byusing linear optics and single photons. Mr.
Maeda advised me to propose the experiment as a PRESTO (Precursory Research for
Embryonic Science and Technology) project of
the Japan Science and Technology Corporation (JST).
With the financial support and encouragement by JST and Mitsubishi Electric, I devoted myself to the experiment from 1995
and succeeded in demonstrating the DeutschJozsa algorithm in 1998 1).
During that period, I also had a chance tovisit Prof. Yoshihisa Yamamoto's laboratory atStanford University for nine months. The staythere was very impressive. I worked on thedevelopment of photon detectors that had
88% quantum efficiency 2) and also the ability to distinguish the number of incident photons 3) with Dr. Jungsang Kim. The friendshipI had with the group members at Stanford remains a treasured memory of mine.
During the course of theseresearches, I became fascinated by basics experiments inquantum optics, rather thanthose aiming at producing future products. Fortunately, I
had a chance to move to anacademic position at Hokkaido University in 1999.

living there. Hokkaido University is in the central part of Sapporo.
My house sits seven km south of the University. I usually take a subway ( not crowdedso much ) to Sapporo station for 10 minutes
each morning, and walk 15 minutes to thelaboratory. I really like the passage through agrove of white birch on the university campus. In winter, everything is covered withsnow, and the contrast between the blue ofthe sky and the white of the snow and trees
in the very pure air is wonderful. However, inorder to enjoy this beauty, I have to endurecold down to minus ten degrees Celsius. The
temperature in summer is usually 20 to 30
degrees Celsius, and that's very comfortable.
The island is also famous for its delicious
foods, beautiful nature and many Onsen (hotsprings spas). Some people in our researchgroup like hiking. This summer, we visited
mount Tokachi-dake (2077m) and enjoyed
its surrealistic volcano landscape and beautiful alpine plants (see picture). Needless to say,Sapporo and Hokkaido
UniversityHokkaido is the second
largest and most northern ofJapan's four main islands. Thecapital city of Hokkaido is Sapporo with two million people

At the starting point of the trail to Tokachi-dake: Matsuo, Ishii, Kojima, andTakeuchi. (From the left)

JSAP International No.7 (January 2003)

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Young Scientist
I wish to be a photon juggler

we enjoyed an outdoor Japanese-style hotspa, also.

My research activity
I am interested in the quantum information technologies using photons. As weknow, the true description of the nature isgiven not by classical ( Newtonian ) theory,
but by quantum theory. In the field of quantum information 4), people are trying to reconstruct the information theory based on
quantum physics. There are two main applications that attract people. One is quantum
cryptography, which enables us to transfer
a "random number key" without any possibility of its being intercepted. The other isquantum computation, which enables us toperform massive parallel data processing in
extremely large Hilbert space.
Currently, we are trying to achieve quantum information processing by using photons. I demonstrated a quantum algorithm
using single photons and linear optics in1998 1). At that time, our method had a weak
point in that the number of optical modes
increased exponentially when the number ofrequired qubits increased.

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JSAP International No.7 (January 2003)

Recently, Knill, Laflamme and Milburn
proposed a scheme to create a quantum
computer by using linear optics, single protons, and multi-photon distinguishable detectors where the number of modes scales
linearly with the number of qubits 5). This proposal represents tremendous progress.
Based on their ideas, our research group
has also suggested a more practical method
for constructing both a quantum gate 6), anda quantum filter that can create entanglement between single photons 7).
Currently, our research group in Hokkaido University is also working on achieving
single photon sources 8), and single photon
quantum phase gates by using cavity quantum electrodynamics 9).

Conclusion
I hope you found some points of interestin this article. Your impressions, comments
and questions are welcomed; please sent
them to takeuchi@es.hokudai.ac.jp . Youcan get additional information at our website: http://optsys.es.hokudai.ac.jp/indexe.html

References1 ) S. Takeuchi, Phys. Rev. A, 61 (2000) 052302,and S. Takeuchi, Phys. Rev. A, 62 (2000)
032301.
2 ) S. Takeuchi, J. Kim, Y. Yamamoto, and H. H.
Hogue, Appl. Phys. Lett., 74 (1999) 1063.
3 ) J. Kim, S. Takeuchi, Y. Yamamoto, and H. H.
Hogue, Appl. Phys. Lett., 74 (1999) 902.
4 ) M. A. Nielsen and I. L. Chuang, Quantum
Computation and Quantum Information ,(Cambridge University Press, Cambridge, UK2000 )5 ) E. Knill, R. Laflamme, and G. Milburn, NatureLondon 409, (2001) 46.
6 ) H.F. Hofmann and S. Takeuchi, Phys. Rev. A,66, (2002) 024308
7 ) H.F. Hofmann and S. Takeuchi, Phys. Rev. Lett.
88 (2002) 147901
8 ) S. Takeuchi, Optics Lett., 26 (2001) 843.
9 ) H. F. Hofmann, K. Kojima, S. Takeuchi and K.
Sasaki: arXiv.org/quant-ph/0208029